Ion sources are employed to create the ions used to perform various semiconductor processes, such as ion implantation. In many embodiments, a dopant species, often in the form of a gas is introduced into the arc chamber of an ion source. The dopant species is then excited, such as by high energy electrons that have been accelerated across a potential or by radio frequency (RF) energy, to create ions. These ions are then extracted from the arc chamber in the form of an ion beam.
In certain embodiments, the dopant species may be in the form of a solid, which is vaporized prior to its use in the arc chamber of the ion source. For example, a solid material may be disposed in a crucible or tube, which is part of a vaporizer. The crucible is then heated, such as by an external heating coil. Vapor then exits the crucible through a nozzle, where it is guided toward the arc chamber of the ion source. In certain embodiments, the crucible may be disposed within the ion source itself.
One issue associated with vaporizers is condensation. As the crucible is heated, the solid material disposed within reaches a temperature sufficient to produce a needed vapor pressure of the solid material. However, as the vaporized gas exits the crucible, the gas may encounter regions which are at a lower temperature than that inside the crucible. If this lower temperature is less than the temperature of the solid material containing the dopant, the vapor may begin to condense. Condensation may reduce or even inhibit the flow of vapor to the ion source.
In addition, in certain embodiments, the nozzle of the vaporizer may be positioned lower than other portions of the vaporizer. In other words, the height of the nozzle may be less than other portions of the vaporizer. This may be problematic if the dopant containing species is in the liquid state. In certain applications, the solid material containing the dopant may have a melting temperature lower than the temperature necessary to produce a useable vapor pressure. In this case, the temperature of the crucible may be greater than the melting temperature. In such instances, the material may melt, and the vapor is generated from the liquid. This liquid may then flow toward the nozzle, which is lower in height than these other portions of the tube. This liquid may cause the vaporizer to clog. Also, it may be undesirable for the liquid to enter the arc chamber of the ion source.
In summary, current vaporizers suffer from two major drawbacks. The first is a temperature gradient across the vaporizer that causes some portions of the vaporizer to be cooler than other portions. This may cause some of the vapor in the vaporizer to condense and block the flow of the remaining vapor. The second issue is spatial orientation. As stated above, if the nozzle is lower in height than the rest of the crucible, liquid may flow toward the nozzle causing clogging.
Thus, it would be beneficial if there were a vaporizer that addressed these issues associated with condensation. It also would be advantageous if such a vaporizer could be deployed in a number of different orientations without condensed material flowing out of the vaporizer or clogging.